System and method for measuring free-space parameters of an antenna

ABSTRACT

Disclosed is a system for measuring free space properties of an antenna. The system includes an analyzer adapted to obtain from an antenna supported in the air by an aircraft, at least one property of the antenna, and to determine at least one property of the antenna. The system also includes a telemetry unit adapted to relay information from the analyzer to a ground station.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation under 37 C.F.R. § 1.53(b)(1) ofcommonly owned U.S. patent application Ser. No. 15/618,545 to Howard, etal. entitled “System and Method for Measuring Free-Space Parameters ofan Antenna” filed on Jun. 9, 2017. The present application claimspriority under 35 U.S.C. § 120 to U.S. patent application Ser. No.15/618,545, the disclosure of which is hereby incorporated by referencein its entirety.

BACKGROUND 1. Field

Example embodiments relate to systems and methods for measuring thefree-space parameters of an antenna.

2. Description of the Related Art

Common methods for measuring free-space or near free-space parameters ofan antenna employ anechoic chambers, elevated ranges, compact ranges,and slant ranges. Each of these methods have variousadvantages/disadvantages.

Anechoic chambers typically have walls, a ceiling, and a floor linedwith special electromagnetic wave absorbing materials. The specialelectromagnetic wave absorbing materials are often in the form of jaggedtriangles designed to reflect electromagnetic waves in random directionsto suppress their effects during a measurement step. Anechoic chamberssuffer several drawbacks. First, the special electromagnetic waveabsorbing materials are relatively expensive. Second, the materialscannot fully eliminate reflections in the chamber. Third, anechoicchambers are generally only usable for antennas having frequencies of300 MHz or higher. Fourth, the chambers are generally designed only forsmall antennas.

Elevated ranges utilize a source antenna and a test antenna mountedabove the ground. The antennas can be on towers, buildings, hills, ormountains, however, a line of sight between the antennas must beunobstructed. Reflections from the ground are undesirable, as such,artisans generally locate where the significant reflections occur andattempt to minimize the reflections from these surfaces. For example, RFabsorbing materials are often provided at the reflection locations inorder to minimize their effect. This, of course, can add significantcost to the test and does not guarantee ground reflections will beeliminated.

Compact ranges employ a source antenna placed in a far field of a testantenna. This technique may be applied indoors or outdoors. For indoorchambers there is often not enough separation between the source antennaand test antenna to place the test antenna in a far field. To compensatefor this, a source antenna is often oriented towards a reflector, forexample, a parabolic mirror, whose shape is designed to reflect thesource's wave in an approximately planer manner. A length of thereflector is typically several times larger than the test antenna. Inthis technique, care must be taken to offset the source antenna so thatit is not in the way of the reflected wave pattern. Furthermore, caremust be taken to prevent any direct radiation from the source to thetest antenna. Compact ranges are generally usable for only smallantennas.

Slant ranges use a test antenna mounted on a relatively large structure,for example, a fiberglass tower. A main radiating beam from the testantenna is directed to a source antenna which may be on the ground. Sizeand weight of the test antenna is restricted to the capability of thetower and interaction with the materials used to construct the tower. Inmost cases, the tower must be made of a non-conductive material whichhas a higher cost associated with it.

While the above methods are usable for determining free-space parametersof an antenna, each suffers errors associated with phase, amplitude, andripples due to their deviations from ideal test conditions. What isneeded is a new and improved method of measuring free-space propertiesof an antenna that does not suffer the above mentioned drawbacks.

SUMMARY

Example embodiments relate to systems and methods for measuringfree-space parameters of an antenna.

In example embodiments, a method for measuring free space properties ofan antenna may include supporting the antenna above the ground by anaircraft and using an analyzer to determine at least one property of theantenna while the antenna is suspended in the air. In exampleembodiments, the method may further include a flying drone around theantenna while the antenna is suspended and using the drone to takemeasurements of the antenna.

BRIEF DESCRIPTION OF THE DRAWINGS

Example embodiments are described in detail below with reference to theattached drawing figures, wherein:

FIG. 1 is a view illustrating near and far fields associated with anantenna;

FIG. 2 is a view of a system in accordance with example embodiments;

FIG. 3 is a close up view of the system showing a flight pattern of adrone in accordance with example embodiments;

FIG. 4 is a view of a drone in accordance with example embodiments;

FIGS. 5A-5C are views of example flight patterns in accordance withexample embodiments;

FIG. 6 is a view of another system in accordance with exampleembodiments;

FIG. 7 is a flowchart illustrating an example method of measuringfree-space properties of an antenna; and

FIG. 8 is a flowchart illustrating an example method of measuringfree-space properties of an antenna.

DETAILED DESCRIPTION

The drawings in this application show one or more example embodiments ofthe invention and are provided to aid those skilled in the art tounderstand the invention. The invention, however, may be embodied indifferent forms and should not be construed as limited to the exampleembodiments illustrated in the drawings. In the drawings, the sizes ofcomponents may be exaggerated for clarity.

In this application various elements may be described as being “on,”“connected to,” or “coupled to” another element. Elements described asbeing “on”, “connected to” or “coupled to” another element can bedirectly on, directly connected to, or coupled to the other element orany elements there between. Elements described as being “directly on,”“directly connected to,” or “directly coupled to” another element,however, have no intervening element between it and the other element.In this application it is understood the term “and/or” includes any andall combinations of one or more of the associated listed items.

In this application the terms first, second, etc. are used to describevarious elements and/or regions. The terms first, second, etc., however,are not intended to limit the elements and/or regions they areassociated with. Rather, the terms first, second, etc. are only used todistinguish one element and/or region from another element and/orregion. For example, a first element could be termed a second element oreven a third element without departing from the teachings of exampleembodiments.

In this application, spatially relative terms are used for ease ofdescription to describe one element's relationship to another asillustrated in the figures. It is understood that the spatially relativeterms are intended to encompass different orientations. For example, ifa structure in the figures is turned over, elements described as “below”other elements would then be oriented “above” the other elements. Thus,the spatially relative term “below” can encompass both an orientation ofabove and below.

Embodiments are often presented in ideal schematic and cross-sectionviews. As such, examples illustrated in the figures have schematicproperties. Furthermore, the shapes of elements and regions illustratedin the figures merely exemplify shapes and of elements and regions andare not intended to limit the invention.

The description of the example embodiments is not intended to limit thescope of this patent as the claimed subject matter might be embodied inmany ways to include different features or combination of featuressimilar to those described herein. Rather, the description of theexample embodiments is provided to meet statutory requirements.Generally, example embodiments relate to a system and method formeasuring free-space properties of an antenna.

FIG. 1 represents near-field and far-field regions of an electromagneticfield around a transmitting antenna 100. As one skilled in the art wouldreadily recognize, “near-field” behaviors of an electromagnetic fielddominate close to the antenna 100 while “far-field” (radiative)behaviors dominate at greater distances. From a quantitativeperspective, near-field is that part of a radiated field below adistance shorter than the Fraunhofer distance which is defined asd_(f)=2D²/λ where D represents either a diameter or length of an antennaand λ is the wavelength of the electromagnetic field. Of course, oneskilled in the art would also recognize that λ may be calculated as thespeed of light (about 3×10⁸ m/sec) divided by the frequency of theelectromagnetic field in HZ generated by the antenna 100.

FIG. 2 illustrates a system 1000 in accordance with example embodiments.As shown in FIG. 2, the system 1000 includes an antenna 100 suspended byan aircraft 200 via a cable 300. By way of example only, the aircraft200 may be an aerostat (a balloon configured to face a wind) or anothertype of balloon. However, the aircraft 200 may alternatively be apowered aircraft, for example, a helicopter or drone.

In example embodiments, the aircraft 200 may be configured to suspendthe antenna 100 at a sufficient distance above the ground during ameasurement test so that free-space electrical properties of the antenna100 may be measured. As one skilled in the art would readily appreciate,ground effects on an antenna dissipate the farther the antenna is movedfrom the ground. As such, so long as the antenna 100 is sufficientlyseparated from the ground, free space electrical characteristics of theantenna 100 may be obtained. To avoid the effects of groundinterference, the antenna 100 may be suspended about a Fraunhoferdistance, or greater, from the ground.

In example embodiments, an analyzer 105 may be coupled to the antenna100. The analyzer 105 may take measurements of the antenna 100 while theantenna 100 is suspended above the ground. The analyzer 105 may, forexample, be a software defined radio (SDR) vector network analyzer(VNA). In one embodiment, the analyzer 105 includes a power source, forexample, a battery, to power the analyzer 105. This embodiment avoidshaving to run a power cable from a power source, for example, on theground, to the analyzer 105. In example embodiments, the analyzer 105may be arranged at a focal point of the antenna 100 and may be used tomeasure various properties of the antenna 100. For example, the analyzer105 may be configured to measure the S11 parameter of the antenna 100.As one skilled in the art would recognize, the S11 parameter of anantenna is a measurement of reflected power a radio is trying to deliverto the antenna 100. In example embodiments, the antenna 100 may furtherinclude a telemetry unit 107 configured to relay information from theanalyzer 105 to a ground station. In the alternative, the analyzer 105may be connected to a memory, for example, a RAM or ROM chip, to whichmeasurement data may be written and retrieved. Of course, in exampleembodiments, the system 1000 may include both the telemetry unit 107 andmemory.

In example embodiments, a global positioning device 108 may be arrangedwith the antenna 100 so that a position of the antenna 100 may be known.For example, the antenna 100 may include a differential RTK device toprovide GPS coordinates of the antenna 100.

As shown in FIG. 2, the system 1000 may further include a drone 400. Thedrone 400 may be usable to measure various characteristics of theantenna 100. For example, the drone 400 may include equipment usable fordetermining a radiation pattern or gain from the antenna 100 and may bemoved around the antenna 100 to collect this information while theantenna 100 is suspended from the aircraft 200. The drone 400, forexample, may include an antenna 410 along with an analyzer 420 and amini-pc 430 with telemetry to collect the measurement data of theantenna 100. In one embodiment, the analyzer 420 may be a signal houndspectrum analyzer, the antenna 410 may be a Schwarzbeck antenna, and themini-pc 430 may be a Kangaroo PC. These particular elements may beuseful in measuring the amplitude of a signal generated by antennas 100having a frequency range of 9 kHz to about 300 MHz. The analyzer 420 maybe modified, for example, with a downconverter, to increase thefrequency ranges it may analyze to up to 40 GHz. The drone 400 may alsoinclude additional antennas usable in the frequency ranges of 300 MHz toabout 40 GHz. It is understood that one skilled in the art would knowhow to select the appropriate analyzer, antenna, and mini-pc for thefrequency range of measurement based on the antenna 100. Additionally,the drone 400 may include a global positioning device 440 in order todetermine, at any time, the position of the drone 400 relative to theantenna 100. The global positioning device 440, for example, may be adifferential RTK device to provide GPS coordinates where variousmeasurements are made in relationship to the antenna 100. In at leastone nonlimiting example embodiment, the drone 400 may further include asecond GPS system.

In example embodiments, the drone 400 and payload may be calibrated. Forexample, the complete drone system 400 with antenna/analyzer 410/420payload may be calibrated as a system using ANSI C63.5 and CISPR 16-1-1for a three antenna method to obtain the ACF (Antenna Correction Factor)and Gain of the on board antenna that is part of the Drone payload. Anyinfluences the drone 400 will have on the antenna incorporated into thedrone system will be negated with this calibration. To inventor'sknowledge, no one has ever calibrated the whole drone system but onlythe items in the payload separately.

As explained above, the drone 400 may fly around the antenna 100 andtake measurements while the antenna 100 is suspended from the aircraft200. This may allow for relatively accurate free space antenna patternmeasurements of high frequency, very high frequency, ultrahighfrequency, and super high frequency antennas. In one nonlimiting exampleembodiment, the drone 400 may fly in a flight pattern, for example, asemi-hemispherical pattern, around the antenna 100 as shown in FIGS. 2and 3. In at least one embodiment, a center of the pattern is coincidentwith the focal point of the antenna 100. As shown in FIG. 3, the drone400 may take measurements, for example, signal strength from the antenna100, at various points around the antenna 100.

Although FIGS. 2-3 illustrate the drone 400 as flying in a hemisphericalpattern, the invention is not limited thereto. FIGS. 5A, 5B, and 5C, forexample, show other nonlimiting flight patterns. FIG. 5A, for example,illustrates a planer scanning pattern. In FIG. 5A the black dotsrepresent points where the drone may take a measurement, symbols ΔX andΔY illustrate spacings between the measurement points, and symbols “a”and “b” represent a length and a width of the rectangular plane.Although FIG. 5A illustrates the planer flight pattern as having arectangular shape where measurements are taken at regular spacings, theinvention is not limited thereto. For example, measurements may be takenat irregular spacings or logarithmic spacings and the perimeter of theplane may resemble something other than a rectangle, for example, apolygon, a circle, or even an ellipse.

FIG. 5B illustrates a cylindrical flight pattern having a length L wheremeasurements taken by the drone 400, represented by the black dots, forma cylindrical pattern. In FIG. 5B the measurements are illustrated asbeing taken at a regular spacing. For example, in FIG. 5B, ΔZ representsa difference between measurements in a vertical direction and Δφrepresents an angle formed between measurement points. The regularity ofmeasurement points, however, is not meant to limit the invention. Forexample, the measurement points may form a cylinder but may haveirregular spacings. In the example of FIG. 5B, the antenna 100 may besuspended so that its focal point is at a center/middle of thecylindrical pattern.

FIG. 5C illustrates a spherical flight pattern where the measurementpoints taken by a drone 400 are illustrated by black dots. In FIG. 5Csymbols 66 φ and Δθ represent angles taken between measurement points.In the example of FIG. 5C, the focal point of the antenna 100 may be ata center of the spherical flight pattern. In FIG. 5C the measurementpoints are regular, however, the regularity of measurement points is notmeant to limit the invention. For example, the measurement points mayform a sphere but have irregular spacings.

In view of the above, a novel system 1000 for measuring free spaceproperties of an antenna 100 is provided. In this system 1000, theantenna 100 may be tethered to the aircraft 200 via a cable 300. In onenonlimiting example embodiment, the antenna 100 is supported verticallyto position nulls of the antenna's radiation pattern downwards in thedirection of the ground and upwards in the direction of the aircraft200. Positioning the pattern nulls in this axis may minimize interactionbetween the antenna 100 and the ground and between the antenna 100 andthe aircraft 200. In this nonlimiting example embodiment, the aircraft200 may lift the antenna 100 to an elevation so that the ground hasrelatively little influence on the properties of the antenna. Forexample, the aircraft 200 may lift the antenna 100 at least a Fraunhoferdistance from the ground. For example, in one nonlimiting exampleembodiment, the aircraft 200 is an aerostat which is controlled to havea height above the ground of about five hundred (500) feet and a cablelength of about fifty (50) feet above the ground so that a top of theantenna 100 is about four hundred and fifty (450) feet above the ground.Regardless, when the antenna 100 is elevated sufficiently above theground, the analyzer 105 may be operated to determine various electricalparameters of the antenna 100. For example, the analyzer 105 may measurethe S11 component of the antenna which, of course, may be used todetermine a VSWR (Voltage Standing Wave Ratio) and Free Space InputImpedance of the antenna 100. In addition, the antenna 100 may beequipped with a signal source, for example, a continuous wave signalsource, to energize and/or resonate the antenna 100. The drone 400 maybe flown around the antenna 400 to take various measurements of thesignal generated by the antenna 100 to better characterize the antenna100. For example, the drone 400 may take measurements related to theantenna's gain and/or strength at various locations around the antenna100.

In example embodiments the drone 400 may be controlled so that it takesmeasurements in the far field with respect to a signal generated by theantenna 100. By way of example only, if the antenna 100 is generating asignal with a frequency of 400 MHz the wavelength of the electromagneticradiation emitted by the antenna 100 is (3×10⁸ m/sec)/(4×10⁸ Hz)=0.75 m.If the antenna has a length of 10 m the Fraunhofer distance may becalculated as 2*(10 m)²/(0.75 m)=266 m. As such, when the drone 400takes measurements of a signal generated by the antenna 100, the drone400 should take the measurements about 266 m, or larger, from theantenna 100. Of course, this also implies the antenna 100 should also beelevated about 266 m from the ground, or higher, to reduce the effectsof the ground on the antenna 100. In the case of a spherical,hemispherical, or cylindrical flight pattern, the radius of thespherical, hemispherical, or cylindrical flight pattern, in this case,should be about 266 m or larger.

In example embodiments, the aforementioned system and method may be usedto determine the free space parameters of various types of antennas,including, but not limited to, high frequency, very high frequency,ultra high frequency, and super high frequency antennas. For example,dipole antennas, loop antennas, folded dipole antennas, biconicalantennas, log-periodic antennas, bi-log antennas, double ridge waveguide antennas, and horn antennas are just a few examples of antennaswhich may be measured by the above described system and method.

FIG. 6 is a view of a system 2000 usable for measuring the free-spaceproperties of an antenna 100. In FIG. 6, the system 2000 is illustratedas comprising a tower 600 configured to support an antenna 100. Thetower 600 may be comprised of a first substructure 610 and a secondsubstructure 620. The first and second substructures 610 and 620 may bemade of a nonconductive materials, for example, wood or plastic, tominimize the interaction the tower 600 may have on the antenna 100. Theheights of the first and second substructures may vary. In onenonlimiting example embodiment, the first substructure 610 is made ofwood has a height of about forty five feet and the second substructure620 is made of PVC and has a height of about sixty feet. These heightsallow the antenna 100 to be supported off the ground at least onehundred and five feet. This particular example works well for antennashaving a frequency of 50 MHz or higher. Of course, the dimensionsprovided above are merely exemplary and the actual heights of thesubstructures 610 and 620 may vary according to the size and type ofantenna 100 being tested.

The system 2000 may further include a drone 400 configured to measurevarious parameters associated with the antenna 100. In this nonlimitingexample, the antenna 100 may be substantially identical to thepreviously described antenna 100 of FIGS. 2-3 and the drone 400 may besubstantially identical to the previously described drone 400. Forexample, the antenna 100 of FIG. 6 may include an analyzer 105, atelemetry unit 107, a global positioning device 108, and a signalgenerator which may be used as previously described. Similarly, thedrone 400 may include an antenna 410 along with an analyzer 420 and amini-pc 430 with telemetry to collect the measurement data of theantenna 100. However, in the system 2000, it is not critical for theantenna 100 to have a global positioning device 108 or its own powersource since locating of the antenna 100 may be easily ascertained andsince it would be relatively easy to provide a power cable to theantenna 100 due to it being mounted on tower 600. In the system 2000 thedrone 400 may fly around the antenna 100 to collect various measurementsas previously described.

In FIG. 6, the antenna 100 should be spaced far enough from the groundto reduce the effects of the ground on the antenna 100. Thus, as in theprevious example, it is particularly advantageous to size the tower 600so the antenna 100 is supported about a Fraunhofer distance or greaterfrom the ground. A particular benefit of system 2000 over 1000 is thatthe system 2000 may be configured to support relatively large and heavyantennas that may not be easily supported by the aircraft 200.

FIGS. 7 and 8 illustrate flowcharts associated with the instantdisclosure. FIG. 7 for example, illustrates a method 3000 associatedwith measuring various properties of an antenna in free-space. Theseproperties could include VSWR (Voltage Standing Wave Ratio) and FreeSpace Input Impedance of the antenna in free-space. FIG. 8 illustrates amethod 4000 usable for measuring the antenna's gain and/or strength.

In FIG. 7, the method 3000 may begin with a determination 3100 as to howhigh the antenna should be suspended above the ground during themeasurement test. As previously described, this may be determined byusing the Fraunhofer distance which is a function of the size of theantenna (D) and the operating frequency of the antenna. The height ofthe antenna (i.e. distance above the ground) should be about equal to orgreater than Fraunhofer distance. After the height is determined, theantenna should be elevated to the required height 3200 or higher. Thismay be accomplished by attaching the antenna to an aircraft asillustrated in FIG. 2 or by attaching the antenna to a tower as shown inFIG. 6. Once the antenna is supported at the proper height, an analyzeron the antenna may be activated to measure various free-space parametersof the antenna 3300. For example, the analyzer may be, but is notrequired to be, the aforementioned SDR-VNA which can measure the S11 ofthe antenna.

In FIG. 8, the method 4000 may begin with a determination 4100 as to howhigh the antenna should be suspended above the ground during themeasurement test. As previously described, this may be determined byusing the Fraunhofer distance which is a function of the size of theantenna (D) and the operating frequency of the antenna. The height ofthe antenna should be about equal to or greater than Fraunhoferdistance. After the height is determined, the antenna should be elevatedto the required height 4200 or higher. This may be accomplished byattaching the antenna to an aircraft as illustrated in FIG. 2 or byattaching the antenna to a tower as shown in FIG. 6. Once the antenna issupported at the proper height, a signal generator may be activatedwhich causes the antenna to generate a signal 4300. The signal generatormay be the previously described continuous wave signal source, toenergize and/or resonate the antenna. The method may then utilize adrone to fly around the antenna and take various measurements 4400. Forexample, the drone may be equipped with the previously described antenna410, analyzer 420 and mini-pc 430 to collect the measurement data of theantenna 100. The data, for example, may be associated with the amplitudeof a signal generated by the antenna under the influence of the signalgenerator. While taking measurements, the drone may be controlled sothat the measurements are taken at about the Fraunhofer distance orgreater from the antenna to make sure the drone is taking measurementsin the antenna's far field.

The following is an example application of applicant's invention. Inthis example, a user desires to measure the free-space properties of anantenna 100 having a length of about thirty (30) meters and a resonantfrequency of about one hundred (100) MHz. The user desires to use thesystem 1000 of FIGS. 2-4. In order to avoid the effects of the ground,the user calculates the distance the antenna 100 should be suspendedfrom the ground (Step 3100). In one nonlimiting example embodiment, thisdistance may be determined by calculating the Fraunhofer distance whichis defined as d_(f)=2D²λ. In this case, λ of the electromagnetic fieldgenerated by the antenna 100 is about 3.0 m=(3×10⁸ m/s)/(100 MHz) whichis the speed of light divided by the frequency of the electromagneticfield in HZ generated by the antenna 100. The Fraunhofer distance isthen calculated as 600 m=2*(30 m)²/3 m. The user then tethers theantenna 100 to the aircraft 200 and elevates the antenna 100 to a heightof about 600 m or greater (Step 3200). The user then causes theantenna's onboard analyzer 105 to take a measurement of the antenna 100to determine the free-space properties of the antenna 100 (step 3300).For example, the user may send a signal to the antenna 100 which causesthe analyzer 105 to take measurements, for example, an S11 measurementof the antenna 100.

In the event the user wishes to determine additional properties of theantenna 100, for example, the antenna's gain, the user may utilize themethod outlined in FIG. 8. As in the previous example, a height at whichthe antenna 100 should be suspended from the ground may be calculatedusing the Fraunhofer equation (Step 4100) and the antenna 100 may beelevated to this distance above the ground (or greater) by an aircraft(Step 4200). Once properly elevated, the antenna 100 may be controlledto emit a signal (Step 4300). For example, the signal generated by theantenna 100 is controlled by an onboard signal generator which causesthe antenna 100 to generate a signal. The drone 400 may be controlled sothat it flies around the antenna 100 while the antenna 100 generates thesignal to take measurements associated with the signal (step 4400). Thedrone 400, for example, may be programmed with a prerecorded flight pathwhich may be updated in real-time based on the position of the drone 400with respect to the antenna 100, noting the position of the drone 400and the antenna 100 may be known in real time due to the presence of theglobal positioning devices thereon. The drone 400 may then takemeasurements of the antenna's emitted signal and the measurements andposition of the drone 400 can be recorded so the user can understandvarious characteristics of the antenna 100 while it is generating asignal. In this example method, the drone 400 may be controlled so thatmeasurements are taken in the antenna's 100's far field region.

It is understood that example embodiments include elements which arecommon in the art and which may be implemented with the disclosedmethods and devices to fully enable them. For example, the drone 400 mayinclude a communication system which allows the drone 400 to be remotecontrolled by a user. Similarly, the antenna 100 may be fitted with acommunication system which enables a user to control various elementsassociated with the antenna 100. For example, the signal generatorand/or analyzer 105 may be remote controlled by a user so that the usercontrols when the signal generator energizes the antenna 100 or when theanalyzer 105 takes measurements of the antenna 100. As yet anotherexample, a height to which an antenna 100 may be raised may bedetermined by several conventional means including but not limited to,GPS (for example, differential GPS), barometer, and radars. However, adetailed description thereof is omitted for the sake of brevity.

Example embodiments of the invention have been described in anillustrative manner. It is to be understood that the terminology thathas been used is intended to be in the nature of words of descriptionrather than of limitation. Many modifications and variations of exampleembodiments are possible in light of the above teachings. Therefore,within the scope of the appended claims, the present invention may bepracticed otherwise than as specifically described.

What we claim is:
 1. A system for measuring free space properties of anantenna, comprising: an analyzer adapted to obtain from an antennasupported in the air by an aircraft, at least one property of theantenna, and to determine at least one property of the antenna; and atelemetry unit adapted to relay information from the analyzer to aground station.
 2. The system of claim 1, wherein the antenna issupported so that a distance from a focal point of the antenna and theground is about a Fraunhofer distance or greater.
 3. The system of claim2, wherein the aircraft is an aerostat.
 4. The system of claim 2,wherein the aircraft is a powered device.
 5. The system of claim 2,wherein a parameter is S11.
 6. The system of claim 2, wherein theanalyzer is a vector network analyzer.
 7. The system of claim 2, furthercomprising: a drone adapted to move around the antenna and to takemeasurements of the antenna at a plurality of locations.
 8. The systemof claim 7, wherein the drone measures at least one of radiation andgain from the antenna at a plurality of locations.
 9. The system ofclaim 8, wherein the plurality of locations are disposed in ahemispherical pattern.
 10. The system of claim 7, wherein the dronecomprises a global positioning device to determine a location of thedrone.
 11. The system of claim 7, wherein the plurality of locations areat least a Fraunhofer distance from the antenna.
 12. The system of claim7, wherein the analyzer is adapted to obtain a location of the antennato obtain a plurality of locations of the drone corresponding to theplurality of locations.
 13. The system of claim 1, wherein the antennais tethered to the aircraft via a cable.
 14. The system of claim 1,wherein the antenna is supported vertically to position nulls of theradiation pattern of the antenna downward in a direction of the groundand upwards in a direction of the aircraft.
 15. The system of claim 1,further comprising a tower configured to support the antenna.
 16. Thesystem of claim 15, wherein the tower comprises a first substructure anda second substructure.
 17. The system of claim 16, wherein the first andsecond substructures each comprise electrically nonconductive materialsto minimize electromagnetic interaction between the tower and theantenna.
 18. The system of claim 1, wherein the at least one property isa Voltage Standing Wave Ratio (VSWR).
 19. The system of claim 1, whereinthe at least one property is a Free Space Input Impedance of the antennain free-space.